A term “supercooling” describes a phenomenon that melt or solid does not change even after it is cooled down to a temperature lower than the phase transition temperature at equilibrium state. In general, every material has its own stable state at a given temperature, so if temperature changes gradually, atoms of the substance keep abreast with the changes of temperature while maintaining its stable state at each temperature. However, if temperature changes abruptly, there is not enough time for the atoms to get into a stable state corresponding to each temperature. What happens then is the atoms either keep the stable state at a start temperature, or partially change to a state at a predetermined end temperature then stop.
For example, when water is cooled slowly, it does not freeze for some time even though the temperature is below 0° C. However, when an object becomes a supercooled state, it is a sort of metastable state where the unstable equilibrium state breaks easily even by a very small stimulus or minor external disturbance, so the object easily transits to a more stable state. That is to say, if a small piece of the material is put into a supercooled liquid, or if the liquid is abject to impact on a sudden, it starts being solidified immediately and temperature of the liquid is raised to a freezing point, maintaining a stable equilibrium state at the temperature.
In general, an electrostatic atmosphere is created in a refrigerator, and meats and fishes are thawed therein at a temperature below zero. Besides meats and fishes, fruits are also kept fresh in the refrigerator.
Such technology uses the supercooling phenomenon. According to the supercooling phenomenon, a molten object or a solid in an equilibrium state does not go through the phase change even at temperatures below a phase transition temperature.
As a relevant technology, Korean Laid-Open Patent 2000-0011081 introduced a method and equipment for treating electrostatic field and electrode used therein.
FIG. 1 is a view illustrating a thawing and freshness-keeping apparatus in accordance with a prior art. A cool-keeping device 1 is formed of a heat insulation material 2 and an outer wall 5. A temperature regulator (not shown) is installed therein. A metal shelf 7 installed in the device 1 has a two-layer structure. Objects such as vegetables, meats and marine products that are to be thawed, kept fresh, or ripened are mounted on either layer. The metal shelf 7 is intentionally insulated from the bottom by an insulator 9. In addition, since a high voltage generator 3 can generate 0 to 5000 V of DC and AC voltages, the inside of the heat insulation material 2 is covered with an insulation plate 2a such as vinyl chloride. A high voltage cable 4 for outputting the voltage of the high voltage generator 3 is connected to the metal shelf 7 through the outer wall 5 and the heat insulation material 2.
When a user opens a door 6 installed at the front of the cool-keeping device 1, a safety switch 13 (not shown; refer to FIG. 2) is off to block the output from the high voltage generator 3.
FIG. 2 is a circuit view illustrating a circuit configuration of the high voltage generator 3. 100 V AC is supplied to a primary side of a voltage adjustment transformer 15. Reference numeral 11 denotes a power lamp and 19 denotes an operation state lamp. When the door 6 is closed and the safety switch 13 is on, a relay 14 is operated. This operation state is displayed by a relay operation lamp 12. Relay contact points 14a, 14b and 14c are closed the to the operation of the relay 14, and 100 V AC is applied to the primary side of the voltage adjustment transformer 15.
The applied voltage is adjusted by an adjustment knob 15a on a secondary side of the voltage adjustment transformer 15, and the adjusted voltage value is displayed on a voltmeter. The adjustment knob 15a is connected to a primary side of a boosting transformer 17 on the secondary side of the voltage adjustment transformer 15. The boosting transformer 17 boosts a voltage at a rate of 1:50. For example, when 60 V input voltage is applied, it is boosted to 3000 V.
One end O1 of the secondary side output of the boosting transformer 17 is connected to the metal shelf 7 that is insulated from the cool-keeping device 1 through the high voltage cable 4, and the other end O2 of the output is earthed. In addition, since the outer wall 5 is earthed, even though the user touches the alter wall 5 of the cool-keeping device 1, he or she will not get an electric shock. Meanwhile, in FIG. 1, when the metal shelf 7 is exposed in the device 1, it needs to be maintained in an insulated state, and thus needs to be spaced apart from the wall of the device 1 (the air serves to insulate). Moreover, when an object 8 protrudes from the metal shelf 7 to contact the wall of the device 1, the current flows to the ground through the wall of the device 1. Thus, by attaching the insulation plate 2a to the inner wall, drop of the applied voltage can be prevented. Further, although the metal shelf 7 in the device 1 is not exposed but covered with vinyl chloride, the entire device 1 is under an electric field.
In the prior art, an electric field or magnetic field is applied to a refrigerated stored item so that the item can enter a supercooled state. That is, a complex device for generating an electric field or magnetic field has to be provided to keep the stored item in the supercooled state. Unfortunately, this process takes a lot of power, and the device also mist have a safety device (e.g., an electric field or magnetic field shielding mechanism, a cut-off unit, etc.) additionally to protect a user from high electricity, especially when it is engaged in generation or cutting off the electric field or the magnetic field.
Interestingly though, none of devices in the prior art so far has used a technical configuration to regulate temperature of a supercooled stored item.